When disc brakes are used on the rear wheels of a vehicle, it is necessary to provide a mechanical actuator to institute an emergency and parking brake function of the disc brake assembly. U.S. Pat. No. 3,701,400 illustrates a common used parking brake actuator wherein a ball and ramp mechanism respond to a mechanical input to actuate the rear disc brakes associated with the rear wheels. Adjustments for wear of a friction pad to maintain the functional operation of the parking brake is illustrated in U.S. Pat. No. 3,805,924. This type of actuator functions in an adequate manner, however, after an extended period of use wear may occur and as a result the balls do not uniformly engage the ramps such that unequal loading may occur. With unequal loading a larger input force is required to activate the parking brake.
In an effort to overcome unequal loading forces, a toggle actuator, as disclosed in U.S. Pat. No. 4,544,045, was developed to provide the mechanical force required to activate a parking actuation function for a rear disc brake. In this brake system, an input force is applied through reaction and actuation toggles located in series axial alignment with an actuation piston. This axial force is applied to the actuation piston to move a friction member into engagement with a rotor connected with a wheel of a vehicle and effect the parking brake function. This type of parking brake actuator functions in an adequate manner for most applications, however, under certain conditions with this type parking brake actuator adequate force through the single input may not be large enough to move the friction member into engagement with the rotor through the operation of a service brake. In order to actuate the parking brake it is necessary to apply the parking brake before the release of the service brake which has already positioned the friction pads against the rotor to achieve a desired braking retention force. This type of actuation while functionally operational acceptable does require additional effort on the part of an operator and as a result a better method of actuation of a parking brake through a single and independent operation would be more accepted to a vehicle operator.